Mine is OK as it is, isn't it?
Sure -- if you've got BB, Simon. Otherwise that 120kb difference between the original and optimised versions of your pic can have a signficant impact on loading time for someone with a 56k connection. The filesize of pics is what makes a normal webpage either appear almost instantly, or have you sat around yawning.
Note there is a further penalty with forum pages such as these, since they have to be coded on the fly by the server before they can appear. Therefore anything that can help speed up a page's loading time is all right by me.